I will be adding composting worms to a gravel bed filter that will be in line before my current raft system. The idea of adding growing space and reducing labor when I replace my net tank is very appealing to me. Many months ago I obtained composting worms form several sources and have been increasing their populations. Some of the worms came from a horse manure pile. I have mixed these worms into the various composting bins that I have, which are fed entirely from aquaponics waste. Now that I am getting enough worm population and have my first gravel bed built, I am getting concerned with the quality of my worm stock. My main concern is with the worms that came from the manure pile. How long before manure fed worms are safe to introduce into aquaponics without any concern of bacterial infection that can cause humans harm? Does anybody have experience with this? I am also interested if there are any ratios of gravel bed filter for pounds of fish or growing space? Aloha Chris Coastview Aquaponics
Hi Chris, Recommended ratio....
1lb of fish, per 1 cubic foot (7.48 gals) of F&D media grow beds.
1 lb of fish, per 5 gals of F&D media grow beds.
(minimum recomended depth of media beds....12")
I can understand you wanting do do away with the work involved with the net tank. I'm pressed for space. I can't set up enough media beds for all the filtration. So, I'll be doing a combination........first, the water will go through a solids separator, then through a small amount of media beds (with worms), then last, through a bio-filter (net tank).....of course, then to the troughs/rafts (DWC)
The solids separator does require daily maintenance....but my citrus trees, blue berry bushes and other plants 'love it'.
Chris's system is mostly a raft system so he already has far more fish than the recommended ratio of fish per gravel bed.
With the solids separator it might still work with the gravel beds but keep in mind that sending all the solids through only a small gravel bed usually does cause the gravel bed to get clogged even with worms. How much worms should you add. I don't know, in my media based system I only added a small hand full of worms per bed and they have multiplied. How big is your gravel bed going to be? Will it flood and drain or will it be constant flood? If constant flood, are you providing additional aeration to it?
I think (please don't quote me and forgive me if I'm mistaken, this is from memory) I've seen Rupert give numbers like adding 1500 worms to a grow bed which is like a pound and a half of composting worms per 500 liters of grow bed. I never added that many but I started up slow so the ones I did add had time to reproduce before my fish load got too big.
If it's been more than six weeks since your worms were exposed to fresh manure, then I would probably feel safe enough adding the worms (not the compost they are in) to your system but that is my personal comfort zone and not any scientific advice.